Conventionally, a seatbelt retractor provided for a vehicle seat and the like has employed a pretensioner mechanism that takes up a webbing so as to ensure safety by efficiently restraining a vehicle occupant at the time of emergency such as vehicle collision and the like.
A take-up drum for winding a webbing includes flange portions formed so as to extend in its radial direction, at both ends thereof with reference to its rotational axis direction. A webbing is wound around a drum main body portion provided between the two flange portions. A conjunction body made of a steel material and the like is press-fitted and fixed to a coupling hole portion formed at one of the flange portions with relative rotation with reference to the take-up drum being disabled.
At the time of vehicle collision, a pretensioner mechanism takes up a webbing in a take-up drum so as to restrain a vehicle occupant, as described below.
Gas is generated from a gas generating member so that a rack moves and causes a pinion gear body to rotate. A cam surface is formed on an inner surface of a side portion of the pinion gear body. Clutch rollers are provided between the cam surface and the conjunction body. Along the rotation of the pinion gear body, the clutch rollers are guided to the cam surface and depressed inwardly. As a result, each clutch roller gets engaged between the cam surface and an outer periphery surface of the conjunction body, which enables the pinion gear body and the conjunction body to rotate integrally. Eventually, the take-up drum rotates to take up the webbing.
An example of the above described seatbelt retractor is disclosed in Japanese Patent No. 3934483.
In the above described background art, at the time of vehicle collision, there are interposed some operations from a state where gas is generated from the gas generating member so as to get movement of the rack started till a stage where webbing-take-up operation is started. That is, there is necessity to interpose operations: to rotate the pinion gear body along movement of the rack; to depress the clutch rollers inwardly. During those operations, the webbing is not taken up. Therefore, there is a fear of delay in time from generation of gas at the gas generating member upon detection of vehicle collision till start of webbing-take-up operation for restraining a vehicle occupant. Such delay in emergency operation for ensuring safety by restraining a vehicle occupant is problematic.
Further, at the time of vehicle collision, the clutch rollers get engaged between the cam surface of the pinion gear body and the conjunction body so as to connect the pinion gear body and the conjunction body. This connection enables the pinion gear body and the conjunction body to rotate integrally and the webbing is taken up eventually. In this case, it is difficult to always make length of operational time constant with respect to the course of the pinion gear body's operation; specifically, start of rotation and till completion of engagement with clutch rollers. Positions of the clutch rollers in an ordinary state are not fixed and those of the clutch rollers in an initial rotation state differ individually. That is the reason difference in engagement process occurs. Further, in case plural clutch rollers are used, positions of respective clutch rollers differ and an idling state continues until at least three clutch rollers get engaged with the engagement axis portion. Further, difference in engagement process may occur due to difference in surface condition, such as dirt, scratch and the like on respective portions. Therefore, it is impossible to make length of operational time constant with respect to the course of the engagement between the clutch rollers and the pinion gear body. Further, there may be a fear that engagement therebetween grows tightly depending on webbing-take-up load and driving force cannot be transmitted efficiently. There may occur unevenness in time to start webbing-take-up operation, which is problematic.
Further, for achieving preferable webbing-take-up operation at the pretensioner mechanism, simple and direct driving force transmission mechanism is required. However, in case the take-up drum is directly rotated in the webbing-take-up direction in response to the rotation of the pinion gear body, there arises a problem of mechanical friction as described below.
Mechanical portions that integrally rotate with the take-up drum along rotation of the pinion gear body are made of metal ordinarily, for the convenience of intensity and processability. On the other hand, the housing that supports the take-up drum is also made of metal, ordinarily. Therefore, when the pretensioner mechanism activates in vehicle collision, metallic mechanical portions grind one another and friction grows large. Large friction disturbs smooth operation of the pretensioner mechanism, which is problematic. That is, it is required to realize smooth operation of the pretensioner mechanism by suppressing friction among mechanical portions of the pretensioner mechanism.
In the above-described background art, the pretensioner mechanism is provided on one of outer side plate portions of the housing body. More specifically, main constituent portions of the mechanism that is supposed to rotate the take-up drum at the time of vehicle collision is provided on one of the outer side plate portions of the housing body.
Therefore, with respect to the seatbelt retractor, the number of mechanisms to be mounted outside of the housing increases, which makes size of mechanical units large.
Further, in recent years, there has been thought much of employing advanced functions to previse collision and the like. For implementation of such advanced functions, it is required to leave a room to mount it. In view of such demand, it is inevitable to make mechanical portions implementing existent functions smaller. That is, the seatbelt retractor with pretensioner function is required to reduce mounting volume occupied by the pretensioner mechanism.